rework for the initial CBDOS

src/dos_m65/dos_memchk.s

@@ -0,0 +1,32 @@
+
+;
+; Check if DOS memory is not overwritten
+;
+
+
+dos_MEMCHK:
+
+	; Check for magic string
+
+	pha
+	phx
+
+	ldx #$04
+@1:
+	lda MAGICSTR, x
+	cmp dos_magicstr, x
+	bne @fail
+	dex
+	bpl @1
+
+	plx
+	pla
+	clc 
+	rts
+
+@fail:
+
+	plx
+	pla
+	sec
+	rts